Impact of the colloidal silica particle size on physical vapor deposition tungsten removal rate and surface roughness

Abstract

With the development of sub-0.25 μm technologies, interconnect integration is more sensitive to the surface quality and to the roughness of tungsten-polished layers. Consequently, alumina-based slurries are progressively replaced by silica-based slurries (fumed or colloidal), characterized by much smaller and softer particles. In contrast to the many investigators of alumina-based slurries, only a few investigations have been carried out on the effect of the particle size on the physical vapor deposition (PVD) tungsten, PVD titanium, and thermal oxide removal rates and on the surface roughness after polishing. In this article, we evaluate four different colloidal silica-based slurries having different particle sizes. We find that the most promising slurry is the one with the smallest particle size. We also show that the tungsten removal rate mechanism is probably neither a scratching/indentation nor a surface contact type mechanism, but most likely a mechanism controlled by the growth kinetics of the passivation layer.